Hi all. 
Reading an article about ELO rank I have a question. The probability of the "A" team win is a sigmoid function like 1 / (1 + exp( RankB -RankA))
and after the game we need to update these ranks like Rank_new = Rank_old +- K*(1(0) - probability)  

So the main question is how I can use for example NN( or other algo) for finding "K" parameter to make binary crossentropy minimum. And I hope it musn't be constant (I want to  find dependent from the initial player rating) 

The main my problem that I can't understand is that we need after updating parameters use a new input rank for calculating probability. So every epoch we need to update input